1. Field of the Invention
The present invention relates to separation and purification of (4R, 6R)-4-hydroxy-2,2,6-trimethyl cyclohexanone, which is useful as a material for synthesis of optically active compounds such as pigments, from a mixture of (4R, 6R)-4-hydroxy-2,2,6-trimethyl cyclohexanone and its diastereomer (4S, 6R)-4-hydroxy-2,2,6-trimethyl cyclohexanone.
2. Description of the Prior Art
As a method of separating (4R, 6R)-4-hydroxy-2,2,6-trimethyl cyclohexanone from its diastereomer mixture with (4S, 6R)-4-hydroxy-2,2,6-trimethyl cyclohexanone, there has been known, among others, a method of separation by silica gel column chromatography, a method of separation by counter current distribution and a method of separation by crystallization (Japanese Patent Publication No. 7277/'83).
These separation methods, however, had a number of shortcomings such as requiring a large amount of silica gel and eluent and, in case of the counter current distribution method, a large amount of a highly dangerous solvent such as ether. In case of the crystallization method, a solvent such as ether and an extremely low temperature of approximately -70.degree. C. are required, the product obtainable by the crystallization method is poor and several times of recrystallization are essential, which results in a poor recovery percentage, and thus the method hardly can be said to be economical. Accordingly, there has been a strong need for a separation method industrially advantageous.